Brushless direct current (BLDC) motors are used in applications across many industries including automotive, aerospace, consumer, medical, industrial automation equipment and instrumentation applications. A BLDC motor includes a stator with electromagnetic poles with windings thereon and a rotor with magnet mounted on the surface thereof creating permanent magnetic poles. The stator and the rotor magnetically interact with each other when electric current flows in the windings. BLDC motors require a supply of commutated current to the windings that is synchronized to the rotor position. Phase commutation of current flowing through each of windings is performed at a proper time to form a continuous rotating magnetic field, which can be achieved as a rotor position is correctly recognized.
BLDC motors most commonly use a three-phase configuration with Hall effect sensors imbedded in the motor to define commutation positions for each phase (U, V, W). A conventional three-phase BLDC motor includes a rotor having a plurality of magnetic poles and a stator including U, V and W phase windings. A three-phase BLDC motor has six states of commutation. When all six states in the commutation sequence have been performed, the sequence is repeated to continue the rotation.
Hall effect sensors in BLDC motors are used to commutate the motor based on the change of the Hall sensor signals and for position sensing. The magnetic field sensed by the Hall effect sensors is typically generated by magnets on the rotor of the motor or an additional ring magnet. Hall effect sensors are used as cost effective solutions to sense position.
Commonly BLDC motors have three Hall effect sensors embedded into the stator on the non-driving end of the motor. When the rotor's magnetic poles pass near the Hall effect sensors, they provide a high or low signal indicating if the N or S pole is passing near the sensors. Based on the combination of three Hall effect sensors, the exact sequence of commutation can be determined.
In typical BLDC operations, two of the three phases of a BLDC motor conduct current while the other phase has zero current, i.e. a dead phase, in order for the motor to rotate. A typical three-phase BLDC motor has Hall effect sensors that indicate which two of the three phases are active (i.e. not dead). Hall states (H1, H2, H3) can be used to create a one-to-one relation with rotor phases and the direction which the voltage needs to be applied. There are six possible Hall phase combinations which cover exactly one electric period, therefore, the position resolution using the three phase Hall effect sensors is limited to one sixth of an electric period.
In view of the foregoing disadvantages, it would be advantageous to have a BLDC motor that uses Hall effect sensors and a ring magnet to provide improved resolution position sensing.